Wavelength Division Multiplexing (WDM) is a technique for increasing the bandwidth of optical network communications. WDM allows many (e.g., dozens) of different data signals to be transmitted simultaneously over a single fiber. To keep the signals distinct, WDM manipulates wavelengths of light to keep each signal within its own narrow band. Depending upon the application, WDM is a generally more cost-effective alternative to Time Division Multiplexing (TDM).
The WDM individual signals are multiplexed (not combined) onto a common media—e.g., fiber optic cable—by the use of filters. These filters can be based on varying technologies. The two most common technologies are Arrayed Waveguide Gratings (AWGs), and Thin-Film Filters (TFFs). AWGs are typically less expensive, but larger, and their performance (namely optical insertion loss) has a greater variation due to temperature than a TFF. TFF filters are typically smaller and more consistent across a wider temperature range.
Regardless of the technology, these filters do require a certain amount of physical space that can be costly, either from a leasing or expansion standpoint. This ‘footprint requirement’ necessitates the creation of packaging and housing that provides the greatest number of filters (and therefore signals or services) in the smallest amount of space that can still be serviced on an ongoing basis. For service providers and data centers, the metric for ‘footprint’ is in the ‘rack unit’—1.75″ (vertically) in a 19″ or 23″ standard equipment rack deployed in equipment rooms. The less ‘rack space’ required offers a variety of benefits—from reduced ongoing operational costs associated with the leasing of space in shared or “colocation site”, delaying the need to add additional rack space or equipment rooms, as well as other savings from reduced operational and capital equipment and construction costs. However, a means of addressing the relatively large form-factor of current solutions is desired.